1. Technical Field
The present invention relates to a semiconductor memory apparatus, and more particularly, to a technology for discharging word lines.
2. Related Art
A semiconductor memory apparatus typically receives external power, generates internal voltages having various voltage levels, and operates internal circuits using these internal voltages. In particular, a nonvolatile memory apparatus such as a NAND flash memory generates a plurality of word line control voltages having different voltage levels, and transfers a specified word line control voltage to an assigned word line in each operation mode.
For example, a word line control voltage for a data programming operation has a very high voltage level. If the word line control voltage for data programming is transferred to a word line, corresponding memory cells coupled to the word line are programmed. In order to verify whether the memory cells are precisely programmed after the data programming operation, a word line control voltage for data reading is transferred to the word line to perform a data reading operation, and the data programmed to corresponding memory cells coupled to the word line are outputted. Generally, the data programming operation and the data reading operation are repeatedly performed until the memory cells are precisely programmed. For reference, the data reading operation for verifying whether the memory cells are precisely programmed is called a verify operation.
A word line discharge period occurs between the time period in which the word line control voltage for data programming is transferred to the word line and the time period in which the word line control voltage for data reading is transferred to the word line. In other words, during the word line discharge period after the supply of the word line control voltage of a high voltage level for data programming is interrupted and before the word line control voltage for data reading is supplied, the word line is usually discharged to a ground voltage (VSS).
The word line control voltage for data programming and the word line control voltage for data reading are generated by using charge pumping. When the word line is discharged to the ground voltage (VSS) while the control voltage of a high potential is repeatedly supplied, a substantial time is required to lower the word line to the level of the ground voltage (VSS). Further, a substantial time is required to re-elevate the word line lowered to the level of the ground voltage (VSS) to a specified level. Therefore, the operation of lowering the word line having the high voltage level to the level of the ground voltage and re-elevating the word line having the level of the ground voltage to the specified level is disadvantageous in terms of current consumption.